Low temperature LPCVD PSG/BPSG process

ABSTRACT

A disclosed process use low pressure chemical vapor deposition (LPCVD) of doped oxide film on a substrate. The process includes the steps of providing a substrate in an LPCVD reactor and flowing BTBAS and oxygen into the LPCVD reactor to react on the substrate to deposit an oxide film on the substrate. A doped precursor is flowed into the LPCVD reactor to dope the oxide film as it is deposited on the substrate. This process produces doped oxide film at a relatively low LPCVD reaction temperature.

FIELD OF THE INVENTION

This invention relates to a process of forming oxide films on asemi-conductor substrate and, more particularly, to a low temperatureLPCVD process.

BACKGROUND OF THE INVENTION

Production of semiconductor devices often requires the deposition ofthin dielectric films on wafers. One technique that has been used todeposit thin films on semi-conductor substrates is low-pressure chemicalvapor deposition (LPCVD). It is desirable to have low temperatureprocesses in semiconductor manufacturing to meet the thermal budgetrequirements of the devices.

Previously, the conventional source materials for LPCVD oxide films havebeen SiH₄, Si₂H₆ and TEOS (tetra ethyl ortho silicate). More recently,it has been demonstrated that using BTBAS (bis-tertiary-butyl-aminosilane) as a source material provides a lower temperature LPCVD processfor silicon nitride deposition with improved particulate performance andusable film uniformity.

Despite the previous work on nitride with BTBAS source materials, it isnot known whether a good quality doped oxide can be deposited usingBTBAS as a source such that it can be applied to gap fill applicationssuccessfully or at sufficiently low temperature to be compatible withback end processing.

The present invention is directed to further improvements insemiconductor processing.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a method utilizes BTBASto form doped oxide at relatively low reaction temperatures.

In accordance with another aspect of the invention, a method utilizesBTBAS in gap fill applications.

Broadly, in accordance with one aspect of the invention, there isdisclosed the process of low pressure chemical vapor deposition (LPCVD)of doped oxide film on a substrate. The process includes the steps ofproviding a substrate in an LPCVD reactor and flowing BTBAS and oxygeninto the LPCVD reactor to react on the substrate to deposit an oxidefilm on the substrate. A dopant precursor is flowed into the LPCVDreactor to dope the oxide film as it is deposited on the substrate.

Optionally, a wet or dry anneal using O2 or N2 in the range of 600C-750Cafter deposition can be done to densify the oxide (USG, PSG, BPSG, otherdoped oxides) or to reflow and densify the BPSG film for gap fillapplications.

It is a feature of the invention that the substrate comprises asemiconductor wafer.

It is another feature of the invention that the temperature of the LPCVDreactor is in a range of 400 C to 650 C, and preferably is in a range of420 C to 550 C, and more preferably is below 500 C.

It is another feature of the invention that the dopant precursor isselected from a group consisting of PH₃, TEPO (triethylphosphate), TMPi(trimethylphosphite), B₂H₆, TEB (triethylborate) and TMB(trimethylborate).

There is disclosed in accordance with another aspect of the inventionthe process of LPCVD of doped oxide film on a substrate comprising thesteps of providing a substrate in an LPCVD reactor and flowing BTBAS andoxygen into the LPCVD reactor to react on the substrate to deposit anoxide film on the substrate at a select reaction temperature. Dopantprecursor(s) is/are flowed into the LPCVD reactor to dope the oxide filmas it is deposited on the substrate.

There is disclosed in accordance with a further aspect of the inventionthe process of LPCVD of doped oxide film on a substrate comprising thesteps of providing a substrate in an LPCVD reactor and flowing BTBAS andoxygen into the LPCVD reactor to react on the substrate to deposit anoxide film on the substrate at a select reaction rate. Phosphorousprecursor is flowed into the LPCVD reactor to dope the oxide film as itis deposited on the substrate at a relatively low reaction temperature.

There is disclosed in accordance with yet another aspect of theinvention the process of LPCVD of oxide film for gap fill, asemiconductor substrate defining plural gaps to be filled by the undopedoxide film. The process comprises the steps of providing thesemiconductor substrate in an LPCVD reactor and flowing BTBAS and oxygeninto the LPCVD reactor to react on the substrate to deposit a relativelyconformal oxide film on the substrate.

Optionally, a wet or dry anneal using O2 or N2 in the range of 600C-750Cafter deposition can be done to densify the doped oxide (USG, PSG, BPSG,other oxides) or to reflow and densify the BPSG film for gap fillapplications.

It is a feature of the invention that the temperature of the LPCVDreactor is in a range of 500 C to 650 C in the case of undoped BTBASoxide deposition for gap fill applications.

It is another feature of the invention to flow a dopant precursor intothe LPCVD reactor to dope the oxide film as it is deposited on thesemiconductor substrate to produce a doped glass film. The doped glassfilm is selected from a group consisting of As, B, P, Ge and/or F dopedglass films.

It is a feature of the invention that the temperature of the LPCVDreactor is in a range of 400C to 650C.

Further features and advantages of the invention will be readilyapparent from the specification and from the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a generalized illustration of an LPCVD reactor used in theprocess according to the invention;

FIGS. 2-5 are SIMS curves illustrating test results from semiconductordevices manufactured using both prior processes and the processaccording to the invention; and

FIG. 6 is a sectional view of a semiconductor device having an oxidefilm for gap. fill in accordance with. the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring initially to FIG. 1, a generalized diagram illustrates a lowpressure chemical vapor deposition (LPCVD) reactor 10 for implementingthe processes according to the invention for deposition of doped andundoped oxide films on substrates.

The reactor 10 includes a furnace body 12 to define an interior chamber14. Heating elements 16 surround the chamber 14 to control reactiontemperature. A plurality of wafers 18 are carried on a carrier 20 in thechamber 14.

As is conventional in an LPCVD process, a precursor reactant isintroduced into the chamber 14. Particularly, the precursor comprisesgas flow from one or more gas sources 20 that flow into the chamber 14through a quartz tube 22. The gases interact on the wafers 18 in thepresence of the particular temperature to produce a film on the wafers18.

In accordance with the invention, the reactor 10 implements a method offabricating an oxide film, such as USG (undoped silicate glass) PSG(phospho-silicate glass), BSG (boro-silicate glass) or BPSG(boro-phospho-silicate glass) films. The gas sources include BTBAS andoxygen if undoped silicon dioxide film is deposited. At the same time,other suitable precursors for the dopants are flowed into the chamber 14to dope the silicon dioxide film as the film is deposited, to provide insitu doping. The precursors for phosphorus could be organic or inorganicin nature, such as, for example, PH₃, TEPO and TMPi. The precursors forboron could likewise be organic or of inorganic nature and may be, forexample, B₂H₆, TEB and TMB. The selection of the particular dopantsource is determined by the required deposition rate and temperatureconsistent with both the deposition process and the thermal budget ofthe device.

In the case of phosphorus doped BTBAS films, the deposition rate isenhanced compared to otherwise similar processing conditions.(Comparison of the tables 1 and 2) As is obvious to anyone skilled inthis art, the enhancement of the deposition rate due to the phosphorusdoping can be traded for a lower deposition rate with similar depositionrate. Comparison of table 1 and 2 show that the deposition temperatureis reduced by 75C-100C by the phosphorus doping. The following tables,along with FIGS. 2-5, provide comparative data supporting enhancement indeposition rate and reduction in reaction temperature using phosphorousdoping with BTBAS source material. Particularly, Table 1 illustratestest results for plural test runs using BTBAS source material for USGdeposition. Corresponding FIG. 2 is a Secondary Ion Mass Spectrometry(SIMS) curve for the test run labeled EBM5 in Table 1.

The SIMs data indicates that the C and N compositions are about 1 and1.3% atomic. That is, in spite of the 2:1 atomic ratio of N:Si in theBTBAS precursor, we deposit an oxide with low N and C incorporation.

TABLE 1 Run # IBM1 IBM2 IBM3 IBM4 IBM6 IBM6 IBM7 Run691 AverageDeposition Temperature 575.0 575.0 575.0 575.0 575.0 575.0 575.0 539.2(C) Deposition Pressure (mTorr) 300 150 600 300 300 300 300 1000 BTBASFlow (sccm) 75 75 75 38 150 75 75 150 O2 Flow (sccm) 150 150 150 75 30075 300 300 Average Deposition Rate (A/min) 39.5 18.2 57.6 19.8 55.3 43.034.8 34.5

Table 2 illustrates test results for plural test runs using BTBAS sourcematerial for PSG deposition. Corresponding FIGS. 3 and 4 are SIMS curvesfor the respective test runs labeled 714 and 715 in Table 2.

TABLE 2 Run # Run 714 Run 715 Average Deposition Temperature (C) 453.8509.0 Deposition Pressure (mTorr) 1000 333 BTBAS Flow (sccm) 150 150 O2Flow (sccm) 300 300 10% PH3 Flow (sccm) 150 150 Average Deposition Rate(A/min) 41.2 31.3

Finally, Table 3 illustrates test results for a test runs using TEOSsource material for USG deposition. Corresponding FIG. 5 is a SIMS curvefor the test run labeled 790 in Table 3.

TABLE 3 Run # Run 790 Average Deposition Temperature (C) 650.7Deposition Pressure (mTorr) 1000 TEOS Flow (sccm) 120 Average DepositionRate (A/min) 30.2

Different degrees of deposition rate change or reaction temperaturereduction may occur depending on the types and amounts of the phosphorusdopants introduced.

The SIMs data (FIGS. 3 and 4) indicate that the C and N compositions areabout 0.3% atomic. That is, unexpectedly, we deposit a phosphosilicateglass with trace N and C contents lower than that of the undoped BTBASoxide and only about 10× the background levels measured in the TEOSoxide sample levels found in TEOS oxide.

The etch rate, SIMs, and gap fill data speak to the usefulness of thefilms even though they are deposited at low temperature. See Table 4.

Table 4 provides evidence of the usefulness of the BTBAS oxides bycomparison of etch rates and etch rate ratios (ERR) with those of otherknown oxides. For many applications of oxide films in semiconductordevices, including the gap fill application, an oxide film that etchesat a lower rate is desirable and indicates a denser film. Incorporationof phosphorous is known to increase the etching rate.

The BTBAS undoped oxide etches at a rate lower than that of TEOS undopedoxide in spite of its 75C lower deposition temperature. As HDP (highlydensity plasma) CVD oxide films are known to etch at rates close tothose of thermal oxides, the etch rates of HDP CVD films are also shownfor comparison. The etch rate of the phosphorous doped HDP PSG more thandoubles at a level of 5.4% P.

The etch rate of the BTBAS PSG (run 697) is only about 39% higher thanthat of the HDP (high density plasma) CVD PSG for a comparablephosphorous level. Furthermore, as the ratio of ERR of BTBAS PSG to HDPPSG (1.4-1.6) is less than that of the ratio of ERR of TEOS oxide to HDPUSG (2.1), we expect that the BTBAS PSG to provide an equivalent orgreater improvement in density over TEOS PSG than does BTBAS USG vs.TEOS USG. This analysis speaks to the improved properties of the BTBASPSG in spite of its deposition at a temperature of 500C (150C less thanTEOS oxide).

TABLE 4 Deposition Conditions Etch Rate Property of the film relative toP Etch thermal 10% weight Rate oxide Temp. Pressure BTBAS O2 PH3 TEOS N2Dep Run # % (A/min) ERR (° C.) (mTorr) (sccm) (sccm) (sccm) (sccm)(sccm) IBM 1 BTBAS USG 6.17 2.32 575  300  75 150 IBM 5 BTBAS USG 6.182.32 575  300 150 300 IBM 7 BTBAS USG 6.00 2.25 575  300  75 300 Run 696PH3_Ox_1 4.3 7.84 2.94 500  333 150 300 150 Run 697 PH3_Ox_2 5.5 8.853.32 500  375 150 300 300 Run 699 PH3_Ox_1 4.90 10.36 3.89 475 1000 150300 150 Run 701 PH3_Ox_3 6.37 10.01 3.76 475 1000 150 300 150 LPCVD TEOS65° C. 1 6.80 2.55 650 1000 95 100 LPCVD TEOS 65° C. 2 6.50 2.44 6501000 95 100 HDP PSG 55° C.-60° C. 5.41 6.33 2.38 HDP USG 55° C.-60° C.3.05 1.14 Thermal Oxide 1 2.66 1.00

Thus, in accordance with the invention, PSG and BPSG deposition withBTBAS lower the reaction temperature at comparable deposition rates orenhances deposition rate at comparable temperatures compared to priormethods of making PSG, BSG or BPSG. An estimated BTBAS PSG processtemperature range is 400 C to 650 C. It has been found experimentallythat it is possible to deposit PSG below 500 C as a reasonabledeposition rate. This was performed in an appropriate furnace. At 475 Ca deposition rate of 51.8A/min with measured phosphorus concentration of4 atomic percent was achieved. Assuming 5A/min as the lower cutoffusable deposition rate, and halving of the deposition rate, it wasconcluded that a PSG process as low as 400 C would be feasible. Such lowdeposition temperature enables a different type of application in thesemi-conductor industry, especially in the BEOL (back end of the line)area or MOL (middle of the line) area where the temperature limitationsare major constraints. For example, the conventional undoped TEOSdeposition uses a deposition temperature range of 620 C to 720 C. Thereaction temperature for the PSG or BPSG according to the processdisclosed herein puts the reaction temperature advantageously around 420C to 550 C, which is compatible with many BEOL and MOL processesrespectively.

Thus, the process disclosed herein provides reduction of depositiontemperature by as much as 100 C in BTBAS PSG compared with BTBAS USG(undoped silicate glass or undoped oxide) because phosphorus is addeddeliberately to the process to enhance deposition rate. Likewise, themethod relates to BPSG since phosphorus is likely to enhance thedeposition rate of BPSG due to the presence of phosphorus.

In accordance with another aspect of the invention, BTBAS is used todeposit doped and undoped oxides at low temperatures for gap fillapplications including DT (deep trench) fill, STI (shallow trenchisolation) fill, etc. In any gap fill application it is important toproduce a conformal coating. In accordance with the invention,deposition using BTBAS provides better gap fill and at lower reactiontemperatures.

In tests, it has been found that using BTBAS in gap fill applications,compared to TEOS, at substantially reduced reaction temperatures,provides substantially void-free gap fill. Referring to FIG. 6, across-sectional view illustrates outlining from an SEM photograph of asemiconductor device manufactured using BTBAS in a gap fill application.A substrate 30 defines plural gaps 32 to be filled. Flowing BTBAS andoxygen into the LPCVD reactor 10 of FIG. 1 reacts on the substrate 30 todeposit a relatively conformal oxide film 34, as illustrated. Similarresults were obtained using BTBAS and phosphorous dopant in gap fillapplications.

With USG deposition for gap fill applications using BTBAS the processtemperature range is 500 C to 650 C. With PSG deposition for gap fillapplications using BTBAS the process temperature range is 400 C to 550C. These are lower than the conventional TEOS oxide depositiontemperature of 575 C to 750 C. The reduced process temperature enablesthe application of the BTBAS oxide, both doped and undoped, to gap fillprocess as part of integration schemes. This can be used to provide As,B, P and/or Ge doped glass. This method provides low temperaturevoid-free fill without the need for a subsequent furnace anneal for lowaspect ratio (less than 3) gaps. At higher aspect ratio, a steam annealat 650-750C may be added to densify and/or reflow the BTBAS doped oxide.

Thus, in accordance with the invention, BTBAS is used to provide lowtemperature doped oxides for semi-conductor production, and is used forgap fill oxide films.

Those skilled in the art will appreciate that other oxidation sourcessuch as N₂O, NO, and NO₂ may be added in addition to or as analternative to O₂. Also, BTBAS may be substituted with fluorinatedversions thereof where F is bonded to Si or N.

While the invention has been described in terms of specific embodiments,it is evident in view of the foregoing description that numerousalternative, modifications and variations will be apparent to thoseskilled in the art. Accordingly, the invention is intended to encompassall such alternatives, modifications and variations which fall withinthe scope and spirit of the invention and the following claims.

We claim:
 1. The process of low pressure chemical vapor deposition(LPCVD) of doped oxide film on a substrate comprising the steps of:providing a substrate in an LPCVD reactor; flowing BTBAS and oxygen intothe LPCVD reactor to react on the substrate to deposit an oxide film onthe substrate; and flowing a dopant precursor into the LPCVD reactor todope the oxide film as it is deposited on the substrate, wherein theoxide film includes carbon and nitrogen in concentrations each less than1.3% atomic.
 2. The process of claim 1 wherein the doped oxide filmcomprises a PSG film.
 3. The process of claim 1 wherein the doped oxidefilm comprises a BPSG film.
 4. The process of claim 1 wherein atemperature of the LPCVD reactor is in a range of 400 C to 650C.
 5. Theprocess of claim 1 wherein wherein a temperature of the LPCVD reactor isbelow 500C.
 6. The process of claim 1 wherein the dopant precursor isselected from a group consisting of PH₃, TEPO, TMPi, B₂H₆, TEB and TMB.7. The process of low pressure chemical vapor deposition (LPCVD) ofdoped oxide film on a substrate comprising the steps of; providing asubstrate in an LPCVD reactor; flowing BTBAS and oxygen into the LPCVDreactor to react on the substrate to deposit an oxide film on thesubstrate at a select reaction rate; and flowing a phosphorus precursorinto the LPCVD reactor to dope the oxide film as it is deposited on thesubstrate at a relatively low reaction temperature, wherein the oxidefilm includes carbon and nitrogen in concentrations each less than 0.5%atomic.
 8. The process of claim 7 wherein the select reactiontemperature of the LPCVD reactor is below 500C.
 9. The process of claim7 wherein the select reaction temperature is in the range of 500C-650 Cfor relatively higher deposition rates.
 10. The process of claim 7wherein the phosphorous precursor is selected from a group consisting ofPH₃, TEPO and TMPi.
 11. The process of low pressure chemical-vapordeposition (LPCVD) of oxide film for gap fill on a semiconductorsubstrate defining plural gaps to be filled by the oxide film,comprising the steps of: providing the semiconductor substrate in anLPCVD reactor; and flowing BTBAS and oxygen into the LPCVD reactor toreact on the substrate to deposit a relatively conformal oxide film onthe substrate, wherein the oxide film includes carbon and nitrogen inconcentrations each less than 1.3% atomic.
 12. The process of claim 11wherein a temperature of the LPCVD reactor is in a range of 500C to650C.
 13. The process of claim 11 further comprising the step of flowinga dopant precursor into the LPCVD reactor to dope the oxide film as itis deposited on the semiconductor substrate to produce a doped glassfilm.
 14. The process of claim 13 wherein the doped glass film isselected from a group consisting of As, B, P and/or Ge doped glassfilms.
 15. The process of claim 13 wherein the doped glass film is a PSGdoped glass film.
 16. The process of claim 13 wherein the doped glassfilm is a BPSG doped glass film.
 17. The process of claim 2 wherein theoxide film includes carbon and nitrogen in concentrations each less than0.5% atomic.
 18. The process of claim 15 wherein the glass film includescarbon and nitrogen in concentrations each less than 0.5% atomic.